1. Field of the Invention
The present invention relates to an air-operated valve, more particularly relates to an air-operated valve which suppresses the generation of particles caused when a valve part is seated on a seat.
2. Description of the Related Art
In the production of semiconductors etc., the pure water for washing the silicon wafers and the chemicals and other fluids for etching are required to be extremely high in cleanliness. Specifically, in the road map for next generation semiconductors, which foresees larger scale integration of semiconductors and greater miniaturization of processing, reduction of the line width in circuit patterns to 20 nm or less is being targeted. Therefore, intermixture of particles of 20 nm or larger size in the fluid would have a major impact on the product yield. From this, the members which circulate the fluid while maintaining its cleanliness have great significance.
For example, a conventionally structured air-operated valve is disclosed in FIG. 9 (see Japanese Patent No. 3590572 etc.) This air-operated valve 100 is provided with a valve chamber body 111 which has a valve chamber 120 which forms a controlled fluid inflow part 121 and outflow part 122 and a seat 123 between the inflow part and outflow part and with a valve mechanism 130 which is provided with a valve part 131 which advances toward and retracts from the seat 123 to seal it and a diaphragm 140 which is attached inside the valve chamber 120. A drive mechanism 190 which uses working air which flows out of and into an air port 191 to make the valve mechanism 130 advance and retract to drive and control the opening and closing of the seat 123 is housed inside a housing body 112 on the valve chamber body 111. The drive mechanism 190 is provided with a piston 150 which has a pressure receiving part 156 which is connected to the valve mechanism 130 and which receives working air flowing in from the air port 191 and a spring 180 which biases the piston 150 to the seat 123 side. In the figure, reference numeral 114 is a breathing hole, while 116 is a piston space.
The air-operated valve of FIG. 9 is in a state where the valve part is separated from the seat and the controlled fluid circulates. Here, by lowering the feed pressure of the working air from the air port 191, the pressure which is applied to the pressure receiving part 156 of the piston 150 falls. As a result, the biasing force of the spring overcomes the pressure of the inflowing working air, and the piston 150 descends. In this way, through the valve mechanism 130, the valve part 131 sits on the seat 123.
The force for moving the valve part to the closed state (seated state) is solely provided by the biasing force of the spring. The action of making the valve part rise from the seat in the opening direction (unseated state) is the result of not only the air pressure of the working air which flows in right below the piston, but also the pressure of the controlled fluid which is applied to the valve part and the membrane part of the diaphragm. Therefore, to move the valve part to the closed state, it is necessary to select a spring with a spring force which is larger than the force which the controlled fluid applies to the valve mechanism.
For this reason, the higher the pressure of the controlled fluid, the larger the spring force of the spring that must be used. However, the biasing force of the spring with the large spring force is used to make the valve part sit on the seat, so the impact when the valve part sits on the seat is liable to cause shedding of material from the valve part or the seat.
Therefore, a structure which eases the impact when the valve part is seated has been proposed (see Japanese Patent Publication (A) No. 2005-233298). According to the air-operated valve of Japanese Patent Publication (A) No. 2005-233298, a rubber cushion or other buffer member is interposed below the piston which is connected to the valve part. When the feed pressure of the working air which is fed from the air port changes and the piston descends, the above-mentioned buffer member is sandwiched between the piston and body block below it and is pressed and deformed. Therefore, the impact when the valve part sits on the seat is temporarily eased. After that, along with the descent of the piston, the buffer member further deforms and finally the valve part finishes being seated.
Japanese Patent Publication (A) No. 2005-233298 exhibits a certain effect in suppression of particles generated from the operating valve itself. However, as explained above, there is accompanying deformation of the buffer member which is interposed below the piston. Further, along with use of the buffer member, the buffer member probably will suffer from permanent set. Therefore, the reproducibility of the effect of the buffer member at the time of operation can easily become degraded. In addition, even with the structure of Japanese Patent Publication (A) No. 2005-233298, it is necessary to use a spring with a large spring force commensurate with the pressure of the controlled fluid. Further, it is also necessary to add the amount of force decreased by the buffer member, so use of a spring with a larger spring force is necessary. Further, this means the biasing force of a spring with a larger spring force is used to make the valve part sit on the seat. Due to this, the possibility of material being shed due to the impact when the valve part sits on the seat remains.
As related art, there are the above-mentioned Japanese Patent No. 3590572 and Japanese Patent Publication (A) No. 2005-233298